The present technique most commonly used to prepare substrate surfaces such as semiconductor chips or wafers or the like is known as a chemical mechanical planarization or CMP process. The CMP process may be used to polish, flatten, texture, remove films or otherwise prepare such surfaces. The substrate surfaces are polished or otherwise prepared in a machine typically having a rotatable platen which carries a polishing pad on its surface. The machine also typically has a substrate carrier for holding the substrate during the process. The platen pad and carrier are each manufactured having very high precision flatness, particularly for substrates such as wafers. Substrates are mounted to a separate rotatable polishing head or carrier such that the surface to be prepared is exposed and faces the platen pad. A chemical or abrasive slurry applied to the pad is used to prepare the exposed substrate surface as the carrier is brought into contact with the pad. Downward pressure is usually applied between the carrier and the pad to properly carry out the polishing process.
Substrates are typically held from slipping relative to the carrier by a retainer ring abutting the edge of a substrate. The ring may either be fixed or may float laterally relative to the carrier. The retainer ring ensures that the substrates stay attached to the carrier during the process and until it is desired that they be removed. A positively applied pressure may be applied to the back side of the substrates during the preparation process to ensure prepared surface uniformity. An applied vacuum or negative pressure may also be applied through a process line connected to the carrier to aid in holding the substrates to the carrier during loading and unloading from the machine. A substrate backing film is often applied to the carrier for improving adhesion friction, increasing surface uniformity and as a cushion for the substrates during the process. Once the process is completed, it is necessary to remove the substrates from the carrier.
It is essential to avoid inducing unwanted particle or chemical introduction to the process. During the process, the process line often fills with slurry which may eventually be drawn into the machine's equipment over many process cycles. Though a negative pressure may have been used to hold the substrates to the carrier, once the vacuum is released, the substrates may adhere to the carrier by friction between the substrate and carrier or by fluid surface tension caused by excess abrasive fluid caught between the two. To remove the substrates which are adhered to the carrier, it is common to reverse a negative pressure used to hold the substrates in place during unloading and to apply a positive gas or liquid pressure through the same equipment and process line. The positive pressure breaks the adhesion force between the substrates and carrier.
When the next substrates are to be polished, the pressure in the equipment is again reversed. Any fluids including the wet slurry remaining within the polishing chamber may be drawn into the process line upon negative pressurization of the line. This cycling of the equipment between a positive and negative pressure causes problems. A conventional polishing machine utilizes different fluids for different steps of the process, each of which is delivered and withdrawn through the same lines. Some of the fluids may cause problems as well.
Fluid source equipment is typically disposed remote from the carrier within the polishing machine and coupled to the carrier via a rotary coupling. Conventional rotary couplings connect the rotating shaft of the carrier to the fluid source and include a stationary component coupled to the shaft. The coupling also has a housing with void space between a fluid source line and the carrier fluid process line.
Abrasive or corrosive chemical slurry often is drawn into the process line and enters the coupling becoming trapped in the void space. The slurry gets trapped between the rotating shaft and the shaft bearings, the shaft seals, or the stationary component of the coupling. This causes premature wear, damage and eventually total destruction of the couplings. This also induces deterioration of the coupling components causing particle generation and coupling leakage. Particles may find there way back into the machine and damage substrates during the process. These problems result in high down time for the machine and necessitates frequent maintenance. Though the CMP process has been significantly improved in recent years, little improvements have been made to the machine components.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for an improved rotary coupling for a substrate finishing machine which is more durable and reliable than conventional rotary couplings.